I. Field of the Invention
This invention relates to a suspension rudder bar for an aircraft turbojet with fan hanger, as well as an engine suspension with fan hanger provided with such a rudder bar.
II. Description of Related Art
As illustrated in the side view of FIG. 1, a fan turbojet comprises an air intake 10 extended with a large diameter front casing 11 housing the fan, such a casing being followed downstream with several primary flow casings 12 to 15—with substantially lower diameters—accommodating the compression stages, the combustion chamber, the expansion stages in the turbines and the ejection nozzles. The diameters of the primary flow casings could overall increase slightly from upstream to downstream, that is from the compressors up to the ejection nozzles.
The incoming air is compressed in the fan, then divided in concentric flows, i.e. the primary flow surrounded with a secondary flow. The primary flow is compressed in the compression stages, mixed with a fuel in the combustion chamber for supplying hot gases, then expanded in the turbines so as to drive into rotation the fan and the compression stages, and then ejected for supplying a thrust. But most part of the thrust is formed by the secondary flow being directly ejected either in combination or separately from the primary flow. The flow rate ratio between the two secondary and primary flows, referred to as the dilution rate, enables to increase the engine power. Now, a high ratio between diameters of the fan casing 11 and the primary flow casings 12 to 15 helps to increase the dilution rate.
An engine suspension, generally under a wing, allows the engine load to be transferred to the aircraft by an appropriate intermediary supporting structure. Conventionally, such a support is a rigid pylon 20 with an oblong shape, on which the engine hanging is made with external ferrules of the structural casings: one fastener 21 with the front casing 11 and one rear fastener 22 with the ejection casing 15.
Suspensions are generally designed so as to be <<fail-safe>>, that is able to prevent the aircraft engine from being detached. Such suspensions enable to manage different types of loads: vertical (weight of the engine), axial (thrust), lateral (wing buffeting) loads and torsions (induced by the engine rotating or by a turbine blade being lost). Such suspensions should be able to also accommodate thermal expansions and contractions of the engine, in particular at cruising speed. Such thermal variations induce a not insignificant change in the direction of loads acting on the suspensions.
In <<fail-safe>> isostatic suspensions, the front 21 and rear 22 fasteners comprise rod links 23 and knee links 24 (also see FIG. 2) on the casings 15 and 11, operating in tension in vertical planes perpendicular to the rotation axis X′X of the engine. The loads and the moments between the engine and the pylon are thus transmitted according to the operational reference plane—formed by the rotation axis X′X of the engine, a transversal axis Y′Y and a vertical axis Z′Z−. Such a suspension is for example described in Patent FR 2,925,016.
The fail-safe suspension more specifically comprises connecting rods 30 or other thrust transmission frames between the hub 11a of the front casing 11 and the rear fastener 22 of the ejection casing 15 on the pylon 20, or directly on such a pylon, in the vicinity of the rear fastener.
The top view of FIG. 2 more accurately shows the connecting rods 30a and 30b mounted by knee links 32a, 32b on a rudder bar 40, being itself hinged by a knee link 41 on a central tongue 50 of a plate 51 fastened, as illustrated on FIG. 1, on the rear fastener 22. In such architectures, the rudder bar 40 has a transversal width such that it also enables links 52a, 52b, beyond the connecting rod links 30a, 30b, with lateral extensions 53a, 53b of the plate 51. Should a connecting rod break, for example the connecting rod 30b, the plate 51 rotates anti-clockwise and the play between the extension 52a and the connecting rod 30a is consumed: forces will then be transmitted through the linking knee 32a of the remaining connecting rod 30a. 
However, because of the large transversal width of the rudder bar, being needed for integrating all the links to the plate and to the connecting rods, a large master-couple could be generated in the case of a connecting rod break or of a tension on the fastener or the pylon. Moreover, such large transversal bulk solutions prohibit implementing thin aerodynamic lines.